Compact modular right-angle drive gear aligned actuator

ABSTRACT

A gear drive, such as for an actuator, is a right-angle drive where toothed outer ridge of a face gear is coupled to teeth of a motor output shaft, and a set of planetary gears are engaged with a central sun gear of the face gear. The sun gear and planetary gears are aligned with the motor output shaft. For instance the motor output shaft may be substantially in the same plane with the sun gear and the planetary gears. From another standpoint the axis of the motor output shaft may intersect the sun gear, as well as intersecting a volume that the planetary gears sweep through as the planetary gears engage the sun gear.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 to U.S. ProvisionalApplication 62/962,098, filed Oct. 25, 2019, which is incorporated byreference in its entirety.

FIELD OF THE INVENTION

The invention is in the field of actuators and gear drive trains forproducing rotational movement.

DESCRIPTION OF THE RELATED ART

Rotational actuators are used in a variety of situations. One example isin aerospace vehicles.

In the past hypersonic vehicles have use actuation that is set back aspecific distance from the control surface and control entrance into thevehicle, thereby avoiding the extreme heat present in this entry area.The problem with this is an extended drivetrain is an increase inbacklash and a loss of stiffness and efficiency.

There is thus room for improvement in rotational actuators.

SUMMARY OF THE INVENTION

A modular actuator may be packaged with its own position sensor,drivetrain, and support bearings built in and can be tested forperformance by itself before being integrated in the vehicle. This makesa compound modular actuator (CMA) of the modular variety usable acrossmultiple platforms and readily scalable for different loads and torques.It is readily adaptable to other system simply by changing the motorsize and/or different support bearings and/or gear diameters or numberof gear teeth.

In some environments, such as in a hypersonic flight vehicle, a controlactuator will be exposed to a high level of heating present in thehypersonic environment. Actuators such as those described below willmitigate the heat present on the control surface and surrounding shellof the vehicle and maintain performance against aero and inertial loads.

A gear drive, which may part of a rotational actuator, is a right-angledrive with a motor shaft aligned with a central hub gear of a face gearthat meshes with the motor output shaft.

A gear drive, which may part of a rotational actuator, has a motoroutput shaft that is substantially coplanar with a sun gear andplanetary gears to obtain the highest available efficiency and stiffnessvalues.

A gear drive, which may part of a rotational actuator, has a face gearthat overlaps planetary gears that engage with (mesh with) a central hubsun gear of the face gear that supports the most compact, stiffest, andefficient design.

An actuator includes air gaps in a gear drive, to mitigate or reducemigration of heat through the gear drive.

According to an aspect of the invention, a control actuator (oractuator) includes: a drivetrain; wherein the drivetrain includes a gearset, for example a planetary gear set.

According to an embodiment of any paragraph(s) of this summary, thedrivetrain is a compact drivetrain.

According to an embodiment of any paragraph(s) of this summary, thedrivetrain is a two-stage drivetrain.

According to an embodiment of any paragraph(s) of this summary, theactuator includes a control shaft (or motor shaft) operatively coupledto the drivetrain.

According to an embodiment of any paragraph(s) of this summary, there isa restricted thermal path between the gear set and a distal end of thecontrol shaft.

According to an embodiment of any paragraph(s) of this summary, air gapsare located within the actuator, to restrict thermal transmission.

According to an embodiment of any paragraph(s) of this summary, the airgaps include one or more gaps located between the gear set and thedistal end of the control shaft.

According to an embodiment of any paragraph(s) of this summary, the airgaps include an air gap at a proximal end of the control shaft.

According to an embodiment of any paragraph(s) of this summary, theactuator further including a position sensor.

According to an embodiment of any paragraph(s) of this summary, theposition sensor is located at the distal end of the control shaft.

According to an embodiment of any paragraph(s) of this summary, theactuator further includes an additional position sensor.

According to an embodiment of any paragraph(s) of this summary, the gearset includes a stiff drive gear (or a stiff drive train or a set ofstiff gears).

According to an embodiment of any paragraph(s) of this summary, thedrive gear is coupled to a motor.

According to an embodiment of any paragraph(s) of this summary, the gearset includes a face gear.

According to an embodiment of any paragraph(s) of this summary, one ormore parts of made of stainless steel.

According to an embodiment of any paragraph(s) of this summary, most ofthe parts are made of stainless steel.

According to an embodiment of any paragraph(s) of this summary, one ormore parts are made of titanium, and/or other suitable materials, suchas nickel-chromium-based alloys, for example those sold under thetrademark Inconel.

According to an embodiment of any paragraph(s) of this summary, one ormore parts are made of metal, for instance steel (such as stainlesssteel) or titanium.

According to an embodiment of any paragraph(s) of this summary, theposition sensor is operatively coupled to and/or part of a control loop,such as for control and/or operation of the actuator.

According to an embodiment of any paragraph(s) of this summary, theactuator further includes bearings between relatively rotating parts.

According to an embodiment of any paragraph(s) of this summary, bearingsincludes a control surface support bearing, such as a control finsupport bearing.

According to an embodiment of any paragraph(s) of this summary, at leastone of the bearings is not exposed to a high temperature.

According to an embodiment of any paragraph(s) of this summary, theactuator includes limited-contact-area portions that mitigate thermaltransfer within the actuator.

According to an embodiment of any paragraph(s) of this summary, gearinterfaces between gears of the gear set are one of a group consistingof co-planar, substantially in the same plane, and/or roughly in thesame plane.

According to an embodiment of any paragraph(s) of this summary, theactuator includes and/or operates as a right-angle motor.

According to an embodiment of any paragraph(s) of this summary, thecontrol actuator has a stiffness roughly at least seven times afrequency response, for example being at least six times the frequencyresponse, or at least five times the frequency response, or any rangeusing any of these values (or between the various specified values).

According to an embodiment of any paragraph(s) of this summary, theactuator has a limited rotation, with for example a hard stop providinga limit on rotation.

According to an embodiment of any paragraph(s) of this summary, theactuator has a fully 360-degree rotation.

According to an embodiment of any paragraph(s) of this summary, theactuator is part of a flight vehicle.

According to an embodiment of any paragraph(s) of this summary, theactuator is part of a hypersonic flight vehicle.

According to an embodiment of any paragraph(s) of this summary, theactuator is part of a space vehicle.

According to an embodiment of any paragraph(s) of this summary, theactuator operably coupled to a control surface, and is used to rotatethe control surface.

According to an embodiment of any paragraph(s) of this summary, thecontrol surface includes a flap, elevon, rudder, elevator, aileron, orcanard.

According to an embodiment of any paragraph(s) of this summary, theactuator is part of a thrust reverser.

According to an embodiment of any paragraph(s) of this summary, theactuator is part of a jet engine.

According to an embodiment of any paragraph(s) of this summary, theactuator is part of pump.

According to another aspect of the invention, a method of actuationincludes using the control actuator of any of the other paragraph(s) ofthis summary to control movement of an object.

According to an embodiment of any paragraph(s) of this summary, theobject is a control surface.

According to an aspect of the invention, a gear drive includes: a motorhaving a motor output shaft; and gearing operatively coupled to themotor; wherein the gearing includes: a face gear having a toothed ridgeengaging the motor output shaft, and a central sun gear; and planetarygears engaging the sun gear.

According to an embodiment of any paragraph(s) of this summary, themotor output shaft, the sun gear, and the planetary gears aresubstantially co-planar.

According to an embodiment of any paragraph(s) of this summary, themotor output shaft defines a motor output shaft axis about which themotor output shaft rotates.

According to an embodiment of any paragraph(s) of this summary, themotor output shaft axis substantially perpendicular to a sun gear shaftaxis of the sun gear

According to an embodiment of any paragraph(s) of this summary, the axisintersects the sun gear.

According to an embodiment of any paragraph(s) of this summary, the axisalso intersects a volume swept out by the planetary gears as theplanetary gears rotate about the sun gear.

According to an embodiment of any paragraph(s) of this summary, theplanetary gears are connected to a control output shaft that acts as acarrier for the planetary gears, and that rotates as the planetary gearsorbit around the sun gear.

According to an embodiment of any paragraph(s) of this summary, thecontrol output shaft in part defines an outer air gap between thecontrol output shaft and the part to be rotated, with the first air gapincluding a recess in the control output shaft.

According to an embodiment of any paragraph(s) of this summary, thecontrol output shaft in part defines a central air gap where the sungear meshes with the planetary gears.

According to an embodiment of any paragraph(s) of this summary, the geardrive further includes a part to be rotated, attached to the controloutput shaft.

According to an embodiment of any paragraph(s) of this summary, the partto be rotated is a fin, a control surface, a flap, an elevon, a rudder,an elevator, an aileron, or a canard.

According to an embodiment of any paragraph(s) of this summary, the facegear overlaps the planetary gears.

According to an embodiment of any paragraph(s) of this summary, the facegear has a diameter larger than an overall diameter of a combination ofthe sun gear, and the planetary gears engaged with the sun gear.

According to an embodiment of any paragraph(s) of this summary, themotor output shaft is a part of a two-piece motor shaft.

According to an embodiment of any paragraph(s) of this summary, aposition sensor is operatively coupled to a motor shaft of which themotor output shaft is at least a part.

According to an embodiment of any paragraph(s) of this summary, theposition sensor is at an opposite end of the motor from the motor outputshaft and the toothed ridge of the face gear.

According to an embodiment of any paragraph(s) of this summary, themotor and the gearing are parts of an actuator.

According to an embodiment of any paragraph(s) of this summary, themotor and the gearing are parts of an actuator for a flight vehicle.

According to an embodiment of any paragraph(s) of this summary, themotor and the gearing are parts of an actuator for a hypersonic flightvehicle.

According to an embodiment of any paragraph(s) of this summary, the geardrive is a right-angle gear drive wherein an output rotation isperpendicular to an input rotation.

According to yet another aspect of the invention, a gear drive includes:a motor having a motor output shaft; and gearing operatively coupled tothe motor; wherein the gearing includes: a face gear having a toothedridge engaging the motor output shaft, and a central sun gear; andplanetary gears engaging the sun gear; and wherein the planetary gearsare nested in the face gear, between the central sun gear and thetoothed ridge.

According to still another aspect of the invention, a method rotating acarrier includes: turning a motor output shaft of a motor; rotating aface gear via toothed engagement of the output shaft and a toothed ridgeof the face gear; rotating a set of planetary gears using the rotationof the face gear, with the planetary gears engaged with a central sungear of the face gear; and rotating the carrier, which is coupled to theplanetary gears to rotate about an axis of the central sun gear as theplanetary gears rotate about the central sun gear.

According to an embodiment of any paragraph(s) of this summary, therotating the carrier includes rotating the carrier in a directionperpendicular to a direction of rotation of the motor output shaft.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative embodiments of theinvention. These embodiments are indicative, however, of but a few ofthe various ways in which the principles of the invention may beemployed. Other objects, advantages and novel features of the inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS

The annexed drawings, which are not necessarily to scale, show variousaspects of the invention.

FIG. 1 is an oblique view of a gear drive as part of an actuator, inaccordance with an embodiment of the invention.

FIG. 2 is side sectional view of an actuator according to an embodimentof the invention.

FIG. 3 is a plan view of the actuator of FIG. 2, with portions removedfor illustration purposes.

FIG. 4 is a side sectional view of an actuator according to anotherembodiment of the invention.

FIG. 5 is a high-level flow chart of a method according to an embodimentof the invention.

DETAILED DESCRIPTION

A gear drive, such as for an actuator, is a right-angle drive wheretoothed outer ridge of a face gear is coupled to teeth of a motor outputshaft, and a set of planetary gears are engaged with a central sun gearof the face gear. The sun gear and planetary gears are aligned with themotor output shaft. For instance the motor output shaft may besubstantially in the same plane (substantially co-planar) with the sungear and the planetary gears. From another standpoint the axis of themotor output shaft may intersect the sun gear, as well as intersecting avolume that the planetary gears sweep through as the planetary gearsengage the sun gear.

The arrangement of the gear drive, and in particular the co-planar (orsubstantially co-planar) arrangement of the motor output shaft and thesun and planetary gears, offers many advantages over other priorconfigurations. The gear drive is far more compact than other previousarrangements, offering the potential for a substantial reduction involume that may allow the use of the gear drive in situations wherevolume is at a premium, for instance as a part of an aerospace actuator,such as an actuator for moving a control surface of a hypersonic flightvehicle.

A control actuator, such as for hypersonic flight vehicles (or manyother potential uses), includes a simple low-part compact two-stagedrivetrain that restricts the thermal path of incoming heat andmigration of heat through an integrated control shaft planetary gear setto a stiff drive gear off of the motor, through the implementation of aface gear. The layout is extremely compact and very efficient. Theoperation of the actuator is maintained by locating thermally-sensitiveelectronics for position sensing in such a way as to avoid the hightemperatures being input at the control shaft.

The arrangement of the gear drive provides for good performance in termsof high torque and high stiffness. More broadly, the configurationenhances balance, power, and stiffness. For example, the stiffness maybe about seven times the frequency response of the gear drive. Inaddition, the small rotation inertia of the right-angle motorarrangement allows higher bandwidth for the gear drive.

A position sensor may be located at a far end of the gear drive, on anopposite side of the motor from where the motor output shaft engages theface gear. This configuration may aid in isolating the position sensorfrom heat in the environment where the gear drive output acts, forexample at a control surface of a hypersonic or other high-speed flightvehicle that is actuated using the gear drive. The gear drive oractuator may have other features that act as a barrier or otherwisereduce heat transfer through the device. For example there may be airgaps at locations withing the gear drive or associated parts, forexample an air gap in a control or output shaft of the device where apart to be moved (such as a fin) is connected, and/or around a centrallocation in the gear drive, such as where the sun gear engages theplanetary gears. The relative thermal isolation of the position sensormay facilitate use of the gear train in high-heat environments, such asan actuator for use in a hypersonic or other high-speed flight vehicle.

FIG. 1 shows a general view of a gear drive 10 as a part of a rotationalactuator 12. The gear drive 10 may include a gear set 11, and a motor 13for driving the gear set. The actuator 12 is mounted in a mount object14, and is used to rotate an output object 16. The objects 14 and 16 maybe any of a variety of pairs of objects in which one is to beselectively rotated relative to another. For example the mount object 14may be a fuselage or other part of an aircraft or flight vehicle, suchas a hypersonic or other high speed aircraft or spacecraft, and theoutput object 16 may be a rotatable part of the flight vehicle, such asa control surface such as a fin, or a thrust reverser or other movablepart associated with a jet engine or rocket motor. As another examplethe output object 16 may be a part of a pump, with the part rotatingrelative to the rest of the pump in a free-spinning motion. Otherpossible uses of rotary actuators include land and ground vehicles,where it may be desirable to rotate one part relative to another, forexample controlling the fins of a submarine or the rudder of a ship.

Gear drives described herein, which may be parts of actuators, may beused for a variety of different applications, and a wide range ofcontrol system products. They may be suitable for use inhigh-temperature environments, such as in hypersonic flight vehicles,although they may be used in other circumstances. They can be employed(or adapted to be employed) in missile control applications whichrequire hard stops (limited angular deflections). Alternatively they canbe used in 360-degree free-spinning actuation situations, such as withelevons or flap deployment. Other possible areas of application includejet engine thrust reversal, high-temperature pump systems, and any of avariety of space-limited applications (situations) where thermalenvironment is a concern. It will be appreciated that this is far from acomprehensive list of possible uses for the actuators and gear drivesdescribed herein.

FIGS. 2 and 3 show details of one embodiment, an actuator 20 thatincludes a gear train or gear drive 22. The actuator includes a motor 24that is mounted in a motor casing 28, which may be made of a suitablematerial, such as aluminum, steel, or titanium. The motor 24 is part ofa drivetrain 30 that is operatively coupled to a gear set 32. The gearset 32 includes a face gear 34 and a series of planetary gears 36, 38,and 40.

The motor 24 has a two-part or two-piece shaft 44 (also referred toherein as a “motor shaft” or “control shaft”) that passes through arotor 46 of the motor 24, with the rotor 46 surrounded by a stator 48.The shaft 44 is made up of a first shaft part 52 and a second shaft part54. The first shaft part 52 extends out of a distal end 62 of the motor24, the side of the motor 24 away from the gear set 32. The second shaftpart 54 extends out from the motor 24 at a proximal end 64, toward thegear set 32. The second shaft part 54 acts as a motor output shaft, andthe motor output shaft 54 is toothed, to engage the face gear 34. Theshaft parts 52 and 54 are mechanically joined together inside the stator48, and rotate along with the stator 48 about a motor output shaft axis66.

The motor 24 may be operated as a suitable speed, for example at 8000rpm, 10,000 rpm, or 12,000 rpm. A suitable controller (not shown) may beused to turn the motor on and off to operate the actuator 20.

A position sensor 70 is located at the distal end 62, away from the gearset 32. This helps thermally isolate or thermally insulate the positionsensor 70 from heat generated by and/or transmitted through other partsof the actuator 20. For example a control surface of a hypersonic flightvehicle that is rotated by the gear train 22 may generate heat, which istransmitted back through the gear train 22, the motor 24, and otherparts of the actuator 20. Placing the position sensor 70 on the farthestend of the actuator 20 away from the heat source may allow the actuator20 to be located close to the surface or object it is rotating, asopposed to being located remotely, with additional parts such as alinkage being used to transmit the rotational motion. The motor casing28 is able to withstand heat, for example being made of titanium. Havingthe position sensor 70 at the end of the motor casing or housing 28allows the endurance of the high thermal environment of the hypersonicflight. Such an arrangement may also be advantageous in otherhigh-temperature environments.

The position sensor 70 uses a magnetic sensor 74 to sense rotations ofthe motor shaft 44, in order to track the movement of components of therotational actuator 20. The position sensor 70 may use any of a varietyof other suitable methods and/or mechanisms to track rotation of themotor shaft 44, in order to track movement of the actuator 20. Highertemperature resolvers, a type of analog position sensor, have been usedin place of the magnetic position sensors. Such an alternative mayfurther increase the thermal survivability of the actuator, at theexpense of cost.

External connections to the actuator 20 may be made at the distal end62. Such external connections may include electrical connections forproviding power to the motor 24, control signals for controllingactuation of the motor 24, and communication connections for receivingsignals from the position sensor 70. The external connections mayinclude wires and/or other connections, such as fiber optic connections.

As noted above, the output motor shaft 54 has teeth, which engage (meshwith) corresponding gear teeth of a toothed outer ridge 80 of the facegear 34. The engagement of teeth may be a spur gear engagement or ahelical gear engagement, such that rotation of the motor shaft 44 aboutthe axis 66 causes the face gear 34 to rotate about its face gear axis84. The motor shaft axis 66 and the face gear axis 84 may beperpendicular to each other, or nearly or substantially perpendicular.The toothed outer ridge 80 is at a distance from the face gear axis 84that is much greater than the diameter of the motor output shaft 54,providing a substantial gear ratio at the toothed connection between themotor output shaft 54 and the face gear outer ridge 80.

The face gear 34 has a central hub gear 88 which acts as a sun gear,engaging the planetary gears 36, 38, and 40. The overall diameter of theface gear 34 is greater than the diameter of the combination of the facegear central hub sun gear 88, and the planetary gears 36, 38, and 40.Thus the face gear 34 may be said to overlap the planetary gears 36, 38,and 40.

From another standpoint, the planetary gears 36-40 may be said to benested within the face gear 34. This nesting may be the property bywhich the planetary gears 36-40 are between the sun gear 88, which isradially inward of the planetary gears 36-40, and the face gear toothedouter ridge 80, which is radially outward of the planetary gears 36-40.The planetary gears 36-40 may be located in a cupped region of the facegear 34 that is defined between the central hub sun gear 88 and the facegear toothed outer ridge 80. The produces a gear configuration that iscompact and allows for a coplanar (or substantial coplanar) gearalignment of the gears 34-40 and the shaft axis 66 of the motor shaft44, as described further below.

The planetary gears 36, 38, and 40 each may have a larger diameter thanthat of the sun gear 88. Further, the planetary gears 36-40 sweep aroundthe sun gear 88 at a diameter necessarily greater than that of the sungear 88. Again, as with the engagement between the motor output shaft 54and the face gear 34, there may be a substantial gear ratio at theengagement of the face gear 34 and the planetary gears 36-40, as well aswith a control output shaft or carrier 90 that rotates about the facegear axis 84 as the planetary gears 36-40 rotate about the sun gear 84.

The motor output shaft axis 66 may be substantially perpendicular to asun gear shaft axis of the sun gear 88. The sun gear shaft axis isaligned with and may be considered represented by the face gear axis 84.The term “substantially perpendicular” may mean perpendicular to within0.1 degrees, to within 0.2 degrees, to within 0.5 degrees, to within 1degree, to within 2 degrees, or to within 5 degrees.

The overall gear ratio between the motor output shaft 54 and the controloutput shaft 90 may be any of a great variety of ratios, for examplearound 5000:1. The configuration of gear drives described herein mayallow a large flexibility in gear ratio selection. The gear drive 22 isa two-stage right-angle gear drive, as opposed to more conventionalthree-stage gear systems. Achieving the high gear ratio in a two-stageright-angle gear drive is advantageous, and such an arrangement allowsthe large flexibility in gear ratio selection.

The central hub sun gear 88 may be in line and/or coplanar with themotor shaft 44. For example the shaft axis 66, when extended out fromthe motor shaft 44, may intersect or pass through the sun gear 88,and/or through a volume swept out as the planetary gears 36-40 orbit thecentral hub sun gear 88. The motor shaft axis 66 may be substantiallyco-planar with a plane 89 of the sun gear 88 and the planetary gears 36,38, and 40. The plane of the gears 36-40 and 88 may be taken as theplane that contains the center of the connections between teeth of thesun gear 88 and teeth of the various planetary gears 36, 38, and 40. By“substantially co-planar” it is meant that the offset between the motorshaft axis 66 and the plane 90 may be less than a height of the sun gear88 and/or a height of the planetary gears 36-40. The offset between themotor shaft axis 66 and the plane 89 may be 12.7 mm (0.5 inches) orless, may be 6.35 mm (0.25 inches) or less, may be 2.54 mm (0.1 inches)or less, may be 1.27 mm (0.05 inches) or less, or may be 0.51 mm (0.02inches) or less.

The actuator 20 has many bearings in place to allow various sorts ofrelative movement between adjacent parts of the actuator 20. There maybe bearings 102 and 104 at ends of the motor shaft 44 to allow rotationof the motor shaft 44. A bearing 106 may allow the face gear 34 torotate freely relative to a housing 108 of the actuator 20. The housing108 has a toothed inner surface 110 that engages with (meshes with) theplanetary gears 36-40. A bearing 112 may be located between the housing108 and the control output shaft 90. Roller cage bearings 116, 118, and120 couple respective of the planetary gears 36, 38, and 40, to thecontrol output shaft 90, to allow the planetary gears 36-40 to rotateabout their respective axes as they orbit around the sun gear 88, withthe control shaft 90 thereby also rotating at the same rate about thesun gear 88. That is, the control output shaft 90 rotates about the facegear axis 84.

The control output shaft 90 also has an upper flat thrust washer bearing122 and a lower flat thrust washer bearing 124 to maintain the outputshaft 90 in place. A suitable spacer 130 may be located between thelower washer bearing 124 and a cover 134 through which the controloutput shaft 90 is connected to a part 138 to be rotated by the actuator20, for example a fin or other control surface (or other possibilitiesdescribed elsewhere herein). Fasteners 140 and 142, for example threadedfasteners, may pass through an opening 146 in the cover 134, and may beused to connect the part 138 to the control output shaft 90.

The gear drive 22 also includes air gaps that provide a degree ofthermal insulation, reducing the amount of thermal energy transmittedthrough the gear drive 22. There is a central air gap 160 defined aroundwhere the sun gear 88 meshes with the planetary gears 36, 38, and 40. Inaddition there may be an air gap 162, a recess in the control outputshaft 90, between the fasteners 140 and 142, where the control outputshaft 90 is coupled to the part 138. Actuators such as the actuator 20may rely on limited contact areas and air gaps, such as the air gaps 160and 162, to mitigate the migration of heat through the actuator, duringa flight vehicle mission (or other use of such actuators where heatmigration is a factor). The air gaps 160 and 162 may be omitted whereheat transmission is not an issue (or for other reasons). Conversely theair gaps may be larger, and other intersection materials could be addedto increase or otherwise affect heat migration. As a further alternativeaddition thermal isolation (thermally insulating) material may be placedat various locations, such as between the mounting face on the frontside, the mounting face on the motor to gear stack interface, and themounting of the position sensor itself. This may further decrease theheat transfer.

The actuator housing 108 may have mounting holes 168, used for mountingthe actuator 20 to surrounding structure, such as the structure of anaircraft, spacecraft, watercraft, submarine, land vehicle, or stationaryinstallation. In one embodiment the actuator 20 is an actuator for anaircraft, such as a hypersonic aircraft, but many other uses arepossible for actuators such as that shown, essentially for rotating apart under load in any of a variety of situations.

As noted above, the actuator 20 may include stops (not shown) that limitthe rotational travel of the control output shaft 90 and the part 138.Alternatively the actuator 20 may be capable of a full 360-degreerotation of the control output shaft 90 and the part 138.

The various parts of the actuator 20 may be made of suitable materials.For example the actuator 20 may use mostly standard stainless steelmaterials. or may be made of suitable alloys, for examplehigh-temperature nickel-chromium alloys sold under the trademarkInconel.

Control actuators described herein, the actuator 20 being one example,may have many advantages, including one or more of (in any combination):very compact configuration; modular configuration; no (or mitigated)degradation of performance due to exposure of high temperatures to thecontrol shaft and control fin support bearings; no (or mitigated)degradation of performance due to high temperature intrusion to theposition sensing device that is the primary control loop mechanism forthe actuator. Use of resolvers may also make the system better able towithstand elevated temperatures.

In one possible application the actuator 20 may be a high-performancecompact modular actuator (CMA). The CMA shown in FIGS. 2 and 3 isgreatly reduced in volume relative to prior actuator configurations.Such a reduction in volume may facilitate inclusion of such a CMA insmall flight vehicles, for example in Raytheon's HypersonicAir-breathing Weapon Concept (HAWC).

Advantageously, gear interfaces of the gear drive 22 all fall roughly inthe same plane. While providing almost just half of the original stackheight, this co-planer configuration maximizes balance, power, andstiffness. In a specific embodiment, the stiffness value of the actuator20 is roughly seven times the frequency response, following goodactuator design rules.

Another advantage of actuators such as the actuator 20 is that the smallrotational inertia of the right-angle motor allows higher bandwidth. Theright-angle configuration of the gear drive 22 provides a goodcombination of stiffness and compactness in configuration. Alsoadvantageously, part selection and low part count make the actuator anaffordable solution for precision motion control.

The modularity and/or composability of the actuators described herein,such as the actuator 20, allows them to be adapted for other uses, suchas different types of vehicles, different types or loads, differentspeeds (of control movement as well as vehicle speed), and/or differenttemperatures.

Other actuators are possible using a similar configuration, such as aCMA or actuator 220 shown in FIG. 4. Such actuators may have a differentsize, and/or other different characteristics, from the actuator 20 shownin FIGS. 2 and 3. For instance (to give non-limiting example numbers),the actuator 20 of FIGS. 2 and 3 may have a height of about 5 cm (about2 inches) or less, and a length of less than 20 cm (8 inches). Theactuator 220 of FIG. 4 may be higher and longer, for example having aheight of less than 7.6 cm (3 inches) and a length of less than 23 cm (9inches). Actuators may be resized to fit any of wide variety ofrequirements, including space requirements and performance requirements.

The actuator 220 has many of the features of the actuator 20 (FIG. 2).For example the actuator 220 has a gear train 222 that includes a facegear 234 and planetary gears 236 and 238. A third planetary gear is notvisible in the figure. The face gear 234 has a toothed outer ridge 280that meshes with a motor output shaft 254 of a motor 224. A central hub288 of the face gear 234 acts as a sun gear, meshing with the planetarygears 236-238, which orbit around the sun gear hub 288. This rotates anoutput control shaft 290, which is coupled to an actuated part to berotated. The output control shaft 290 helps define a pair of air spacesor gaps 260 and 262, which may provide a thermal barrier. The actuator220 includes a position sensor 270 at a distal end of the motor 224,with a magnetic sensor 274 for detecting rotation of the motor outputshaft 254. The actuator 220 also advantageously includes a secondposition sensor 276 that has a magnetic sensor 278 for detectingrotation of the face gear 234. The second position sensor 276 may allowincreased functionality, with the addition of other control circuitry.Resolvers may be used in place of one or both of the magnetic sensors274 and 278.

FIG. 5 shows a high-level flowchart of a method 300 of rotating acarrier of an object to be rotated, such as by use of the actuator 20(FIG. 2) or the actuator 220 (FIG. 4). In step 302 a motor output shaftof a motor is turned. In step 304 a face gear is rotated, through ameshing engagement of the motor output shaft and a toothed ridge of theface gear. In step 306 the face gear is used to rotate a set ofplanetary gears that are engaged with (mesh with) a central sun gear ofthe face gear. In step 308 a carrier is rotated, with the carriercoupled to the planetary gears to rotate the carrier about an axis ofthe central sun gear as the planetary gears rotate about the central sungear.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described elements (components, assemblies,devices, compositions, etc.), the terms (including a reference to a“means”) used to describe such elements are intended to correspond,unless otherwise indicated, to any element which performs the specifiedfunction of the described element (i.e., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure which performs the function in the herein illustratedexemplary embodiment or embodiments of the invention. In addition, whilea particular feature of the invention may have been described above withrespect to only one or more of several illustrated embodiments, suchfeature may be combined with one or more other features of the otherembodiments, as may be desired and advantageous for any given orparticular application.

1. A gear drive comprising: a motor having a motor output shaft; andgearing operatively coupled to the motor; wherein the gearing includes:a face gear having a toothed ridge engaging the motor output shaft, anda central sun gear; and planetary gears engaging the sun gear; andwherein the motor output shaft defines a motor output shaft axis aboutwhich the motor output shaft rotates; and wherein the axis intersectsthe sun gear, with the motor output shaft axis substantiallyperpendicular to a sun gear shaft axis of the sun gear.
 2. The geardrive of claim 1, wherein the motor output shaft, the sun gear, and theplanetary gears are substantially co-planar.
 3. The gear drive of claim1, wherein the motor output shaft axis also intersects a volume sweptout by the planetary gears as the planetary gears rotate about the sungear.
 4. The gear drive of claim 1, wherein the planetary gears areconnected to a control output shaft that acts as a carrier for theplanetary gears, and that rotates as the planetary gears orbit aroundthe sun gear.
 5. The gear drive of claim 4, where the control outputshaft in part defines an outer air gap between the control output shaftand the part to be rotated, with the first air gap including a recess inthe control output shaft.
 6. The gear drive of claim 4, where thecontrol output shaft in part defines a central air gap where the sungear meshes with the planetary gears.
 7. The gear drive of claim 4,further comprising a part to be rotated, attached to the control outputshaft.
 8. The gear drive of claim 7, where the part to be rotated is afin, a control surface, a flap, an elevon, a rudder, an elevator, anaileron, or a canard.
 9. The gear drive of claim 1, wherein the facegear overlaps the planetary gears.
 10. The gear drive of claim 1,wherein the face gear has a diameter larger than an overall diameter ofa combination of the sun gear, and the planetary gears engaged with thesun gear.
 11. The gear drive of claim 1, wherein the motor output shaftis a part of a two-piece motor shaft.
 12. The gear drive of claim 1,wherein a position sensor is operatively coupled to a motor shaft ofwhich the motor output shaft is at least a part.
 13. The gear drive ofclaim 12, wherein the position sensor is at an opposite end of the motorfrom the motor output shaft and the toothed ridge of the face gear. 14.The gear drive of claim 1, wherein the motor and the gearing are partsof an actuator.
 15. The gear drive of claim 1, wherein the motor and thegearing are parts of an actuator for a flight vehicle.
 16. The geardrive of claim 1, wherein the gear drive is a right-angle gear drivewherein an output rotation is perpendicular to an input rotation.
 17. Agear drive comprising: a motor having a motor output shaft; and gearingoperatively coupled to the motor; wherein the gearing includes: a facegear having a toothed ridge engaging the motor output shaft, and acentral sun gear; and planetary gears engaging the sun gear; and whereinthe planetary gears are nested in the face gear, between the central sungear and the toothed ridge.
 18. A method rotating a carrier, the methodcomprising: turning a motor output shaft of a motor; rotating a facegear via toothed engagement of the output shaft and a toothed ridge ofthe face gear; rotating a set of planetary gears using the rotation ofthe face gear, with the planetary gears engaged with a central sun gearof the face gear; and rotating the carrier, which is coupled to theplanetary gears to rotate about an axis of the central sun gear as theplanetary gears rotate about the central sun gear; wherein the rotatingthe carrier includes rotating the carrier in a direction perpendicularto a direction of rotation of the motor output shaft.
 19. The method ofclaim 18, wherein the motor output shaft, the sun gear, and theplanetary gears are all substantially coplanar.